Metering valve

ABSTRACT

The present invention relates to a metering valve comprising a valve stem ( 11 ) co-axially slidable within a valve body ( 14 ), the metering valve comprising a metering chamber ( 13 ), wherein the metering chamber is constructed wholly from rigid components.

The present invention relates to improvements in valves for pressuriseddispensing containers.

Pressurised dispensing containers are used for dispensing a wide varietyof products. The pressurised dispensing container is provided with avalve for controlling actuation of the container. The valve may be acontinuous flow valve or alternatively a metering valve in which, uponeach actuation of the valve, a metered quantity of product is dispensed.

The product stored in the pressurised metering chamber typicallycomprises a propellant and an active ingredient as well as othersubsidiary constituents such as solvents, co-solvents and otherconstituents as known in the art. The propellant is typically aliquified propellant having a sufficiently high vapour pressure atnormal working temperatures to propel the product through the valve onactuation by volatilisation of the propellant. Suitable propellantsinclude, for example, hydro-carbon or fluoro-carbon propellants. Inparticular, presently preferred propellants include HFA134a and HFA227.The active ingredient may be any constituent which requires dispensing.Pressurised dispensing containers have found wide-spread use fordispensing active ingredients in the form of pharmaceutical medicamentswhere the medicament is contained in the container in the form of, forexample, a solution or a suspension in the liquified propellant.

Conventional metering valve for use with pressurised dispensingcontainers typically comprise a valve stem co-axially slidable within achamber body defining a metering chamber. “Inner” and “outer” annularseals are operative between the valve stem and the chamber body to sealthe metering chamber therebetween. The valve stem is generally movableagainst the action of a spring from a non-dispensing position, in whichthe metering chamber communicates with bulk product stored in thecontainer, to a dispensing position, in which the metering chamber isisolated from the bulk product and instead is vented to atmosphere so asto discharge the metered quantity of product held in the meteringchamber.

To use a pressurised dispensing container comprising a metering valve asdescribed above, a user first inverts the pressurised dispensingcontainer so that the metering valve is lowermost (the actuationposition) and shakes the apparatus to agitate the product. The agitationhelps to homogenises the product before actuation. This is particularlyimportant where the product comprises a suspension since suchsuspensions may be prone to ‘settling’ over time leading to differencesin the concentration of the medicament throughout the volume of thepressurised dispensing container. The pressurised dispensing containeris then actuated by depressing the valve stem relative to thepressurised dispensing container into the dispensing position. Theproduct in the metering chamber is then vented to atmosphere where itis, for example, inhaled by the user. On release of the valve stem, thespring restores the valve stem to the non-dispensing position, wherebythe metering chamber is re-charged with product from the bulk productstored in the pressurised dispensing container.

A concern with such pressurised dispensing containers, particularlywhere they are used to dispense pharmaceutical medicaments, is theaccuracy of the delivered dose. Variation in the dose can lead to a userreceiving too little or too much medicament. The accuracy of the dosagedispensed is affected by, amongst other factors, the volume of themetering chamber. Variation in the volume of the metering chamber willlead to variation in the metered dose volume. In typical metering valvesthe metering chamber is bounded in part by the inner and/or outer seals.For example the upper or lower face of the metering chamber may beformed, in part or in whole, by the seal surface. It has been found thatthe volume of the metering chamber can be altered due to the deflectionand/or distortion and/or swelling of these seals. Deflection anddistortion of the seals can occur due to the action of the valve stem asit slides to and fro relative to the seals. One example is the meteringvalve of GB2361229A wherein first and second elastomeric seals areprovided for sealing a metering chamber. Whilst a rigid insert 52 isprovided within the chamber this does not wholly define the constructionof the metering chamber and does not prevent flexure and distortion ofthe seals on movement of the valve stem, in particular in directionsaway from the mid-point of the chamber, i.e. when the outer first sealis flexed downwardly on depression of the valve stem.

Swelling of the seals can potentially occur where the seal material isreactive with any of the constituents of the product contained in thepressurised dispensing container.

According to the present invention, there is provided a metering valvecomprising a valve stem co-axially slidable within a valve body, themetering valve comprising a metering chamber, wherein the meteringchamber is constructed wholly from rigid components.

Advantageously, the use of rigid components to construct the meteringchamber allows a more accurate volume of metering chamber to beproduced. The rigid components are not liable to deflection ordistortion during use. The absence of seal materials bounding themetering chamber reduces the likelihood of adverse reactions with theproduct.

Preferably, the metering chamber is constructed wholly from componentsformed from one or more materials selected from polyester, nylon,acetal, or the like, stainless steel, ceramics, glass, or the like.

The metering valve may further comprise inner and outer seals externalto the metering chamber.

Advantageously, the metering chamber may be constructed from only tworigid components. This helps to reduce the number of components whosetolerance affects the volume of the metering chamber. In this way thevariability in the volume of the metering chamber between valves andbetween batches of valves is reduced.

Preferably, the components of the metering chamber comprises one or morestops for limiting axial movement of the valve stem therethrough.

In one embodiment the metering chamber surrounds the valve stem. Themetering chamber may be annular.

The valve body may define a radially outermost surface of the meteringchamber.

The metering valve may further comprise an internal sleeve. The internalsleeve is located concentrically within the valve body. Preferably, theinternal sleeve surrounds the valve stem. Advantageously, the internalsleeve separates the metering chamber from the valve stem.

The metering chamber may be formed between the valve body and theinternal sleeve.

The internal sleeve may define a radially innermost surface of themetering chamber.

Preferably, the internal sleeve comprises a cylindrical portion.

Preferably, the internal sleeve comprises one or more ports for passageof a product into or out of the metering chamber. Preferably, the one ormore ports function as both an inlet to, and an outlet from, themetering chamber in use.

Preferably, the inner seal is carried on the valve stem in slidingsealing contact with a radially innermost surface of the internalsleeve, being external the metering chamber.

A radially directed flange of the internal sleeve may define an outerend surface of the metering chamber.

A radially directed flange of the valve body may define an inner endsurface of the metering chamber.

In another embodiment, the metering chamber is located within the valvestem such that product held in the metering chamber is dischargeabledirectly into the valve stem. Preferably, the metering chamber iscylindrical.

Preferably, the metering chamber comprises one or more ports whichfunction as both an inlet to, and an outlet from, the metering chamberin use. Preferably, the one or more ports are static.

Preferably, the one or more ports are located at an inner end of themetering chamber.

The metering valve may further comprise a seal which is movable relativeto the metering chamber to close off said one or more ports, whereinsaid seal is external to said metering chamber. The seal preferablysurrounds said metering chamber.

The metering chamber may be constructed from an open-ended chamber bodyand a plug. Preferably, the chamber body is substantially located withinthe valve stem.

Advantageously, the metering chamber has no moving parts therein.

The metering chamber may have a volume of up to 300 microlitres.Preferably, the volume is up to 25 microlitres. Advantageously, themetering chamber may have a volume of 10 to 25 microlitres.

Advantageously, the absence of moving parts within the metering chamberallows a chamber to be produced with a very small volume less than 25microlitres. The absence of moving parts also provides for a moreaccurate volume of the metering chamber since the metering chambervolume is defined by fewer components.

In the following description and claims “inner” and “outer” are used todescribe relative positions of components of the metering valve whichare respectively further from or nearer to an outer end 19 of valve stem11 as shown in the Figures.

The valve may be for use in a pharmaceutical dispensing device, such as,for example, a pulmonary, nasal, or sublingual delivery device. Apreferred use of the valve is in a pharmaceutical metered dose aerosolinhaler device. The term pharmaceutical as used herein is intended toencompass any pharmaceutical, compound, composition, medicament, agentor product which can be delivered or administered to a human being oranimal, for example pharmaceuticals, drugs, biological and medicinalproducts. Examples include antiallergics, analgesics, bronchodilators,antihistamines, therapeutic proteins and peptides, antitussives, anginalpreparations, antibiotics, anti-inflammatory preparations, hormones, orsulfonamides, such as, for example, a vasoconstrictive amine, an enzyme,an alkaloid, or a steroid, including combinations of two or morethereof. In particular, examples include isoproterenol[alpha-(isopropylaminomethyl)protocatechuyl alcohol], phenylephrine,phenylpropanolamine, glucagon, adrenochrome, trypsin, epinephrine,ephedrine, narcotine, codeine, atropine, heparin, morphine,dihydromorphinone, ergotamine, scopolamine, methapyrilene,cyanocobalamin, terbutaline, rimiterol, salbutamol, flunisolide,colchicine, pirbuterol, beclomethasone, orciprenaline, fentanyl, anddiamorphine, streptomycin, penicillin, procaine penicillin,tetracycline, chlorotetracycline and hydroxytetracycline,adrenocorticotropic hormone and adrenocortical hormones, such ascortisone, hydrocortisone, hydrocortisone acetate and prednisolone,insulin, cromolyn sodium, and mometasone, including combinations of twoor more thereof.

The pharmaceutical may be used as either the free base or as one or moresalts conventional in the art, such as, for example, acetate,benzenesulphonate, benzoate, bircarbonate, bitartrate, bromide, calciumedetate, camsylate, carbonate, chloride, citrate, dihydrochloride,edetate, edisylate, estolate, esylate, fumarate, fluceptate, gluconate,glutamate, glycollylarsanilate, hexylresorcinate, hydrobromide,hydrochloride, hydroxynaphthoate, iodide, isethionate, lactate,lactobionate, malate, maleate, mandelate, mesylate, methylbromide,methylnitrate, methylsulphate, mucate, napsylate, nitrate, pamoate,(embonate), pantothenate, phosphate, diphosphate, polygalacturonate,salicylate, stearate, subacetate, succinate, sulphate, tannate,tartrate, and triethiodide, including combinations of two or morethereof. Cationic salts may also be used, for example the alkali metals,e.g. Na and K, and ammonium salts and salts of amines known in the artto be pharmaceutically acceptable, for example glycine, ethylenediamine, choline, diethanolamine, triethanolamine, octadecylamine,diethylamine, triethylamine,1-amino-2-propanol-amino-2-(hydroxymethyl)propane-1,3-diol, and1-(3,4-dihydroxyphenyl)-2-isopropylaminoethanol.

The pharmaceutical will typically be one which is suitable forinhalation and may be provided in any suitable form for this purpose,for example as a solution or powder suspension in a solvent or carrierliquid, for example ethanol, or isopropyl alcohol. Typical propellantsare HFA134a, HFA227 and di-methyl ether.

The pharmaceutical may, for example, be one which is suitable for thetreatment of asthma. Examples include salbutamol, beclomethasone,salmeterol, fluticasone, formoterol, terbutaline, sodium chromoglycate,budesonide and flunisolide, and physiologically acceptable salts (forexample salbutamol sulphate, salmeterol xinafoate, fluticasonepropionate, beclomethasone dipropionate, and terbutaline sulphate),solvates and esters, including combinations of two or more thereof.Individual isomers such as, for example, R-salbutamol, may also be used.As will be appreciated, the pharmaceutical may comprise of one or moreactive ingredients, an example of which is flutiform, and may optionallybe provided together with a suitable carrier, for example a liquidcarrier. One or more surfactants may be included if desired.

Embodiments of the present invention will now be described by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a metering valve according to afirst embodiment of the present invention in a non-dispensing position;

FIG. 2 is a cross-sectional view of the metering valve of FIG. 1 in adispensing position;

FIG. 3 is a cross-sectional view of the metering valve of FIG. 1undergoing “pressure filling”;

FIG. 4 is a perspective view of a part of a valve stem of the meteringvalve of FIG. 1;

FIG. 5 is a cross-sectional view of a part of an inner seal of themetering valve of FIG. 1;

FIG. 6 is a cross-sectional view of a metering valve according to asecond embodiment of the present invention in a non-dispensing position;

FIG. 7 is a cross-sectional view of the metering valve of FIG. 6 in adispensing position; and

FIG. 8 is a cross-sectional view of the metering valve of FIG. 6undergoing “pressure filling”.

As shown in FIG. 1, a metering valve 10 according to a first embodimentof the present invention includes a valve stem 11 which protrudes fromand is axially slidable within a valve body 14. An internal sleeve 12 islocated within the valve body 14 in which sleeve 12 the valve stem 11slides. The internal sleeve 12 and valve body 14 define therebetween anannular metering chamber 13.

The metering valve 10 is located within a canister (not shown) andcloses off an open end of the canister to form a pressurised dispensingcontainer. The valve body 14 and internal sleeve 12 are held in positionwith respect to the canister by means of a ferrule 15 which is crimpedto the top of the canister during assembly. The pressurised dispensingcontainer contains a product to be dispensed. Slots 31 are provided inthe valve body 14 to allow passage of bulk product from within thecanister into the interior of the valve body 14.

The internal sleeve 12 is generally cylindrical in shape and comprises atubular portion 12 a and a radially outwardly-directed flange 12 b atits outer end. A radially outermost, external face 40 of the internalsleeve 12 defines a radially innermost, internal cylindrical surface 40of the metering chamber 13. An upper face 41 of the metering chamber 13is defined by an innermost face of the flange 12 b. The valve body 14defines an external cylindrical surface 42 and lower face 43 of themetering chamber 13. The internal sleeve 12 and valve body 14 are bothformed from rigid materials such as acetal, nylon, polyester or thelike.

The internal sleeve 12 is provided with one or more, preferably two,radial ports 23 which allow passage of product from an interior of theinternal sleeve 12 into the metering chamber 13 and vice versa, in use,as will be described below. The radial ports 23 are located at theinnermost end of the metering chamber 13 such that when the valve isinverted for use the radial ports 23 are uppermost. The size of theports 23 is sufficient for the metering chamber 13 to rapidly fill oninversion of the valve. Locating the ports 23 at the innermost end ofthe chamber 13 prevents gas bubbles being trapped in the chamber 13 oninversion of the valve. After actuation the valve would be restored tothe orientation shown in FIG. 1. Product is not stored in the meteringchamber 13 between actuations thereby preventing dehomogenisation of theproduct due to settling and other effects.

The metering chamber 13 has a predefined volume for a single dosage ofthe product to be dispensed. Preferably, the volume of the meteringchamber is between 10 and 300 microlitres. More preferably the meteringchamber has a volume of 10 to 25 microlitres.

Sealing between the valve body 14 and canister is provided by an annulargasket 16. The ferrule 15 has an aperture 28 through which the valvestem 11 protrudes.

An outer seal 17, typically of an elastomeric material, extends radiallybetween the valve stem 11 and the valve body 14. The outer seal 17 iscompressed between the flange 12 b of the internal sleeve 12, the valvestem 11, the valve body 14 and the ferrule 15 so as to provide positivesealing contact to prevent leakage of the contents of the meteringchamber 13 and canister between the valve stem 11 and the aperture 28,although the seal 17 allows sliding movement of the valve stem 11 withrespect to the seal 17.

The valve stem 11 defines a hollow bore 4 having a discharge outlet 3 atits outer end. The opposite end is closed off at an inner end 26. One ormore discharge ports 21 extend radially through a side wall of the valvestem 11 providing communication between the bore 4 and atmosphere whenthe valve stem 11 is in the non-dispensing position shown in FIG. 1. Thedischarge port 21 is located outside the valve body 14 in thenon-dispensing position of FIG. 1 but is moveable to within the valvebody 14 as will be described below. The inner end 26 of the valve stem11 is provided with a conical portion 26 a.

The valve stem 11 is provided with two diametrically opposed projections8, as most clearly shown in FIG. 4. Each projection 8 runs within alongitudinal channel 7 formed on the internal surface of the internalsleeve 12. Each projection 8 comprises two pips 50 having a gap 51therebetween. The pips 50 extend into the channel 7. The valve stem 11is provided with two longitudinal grooves 53 on its exterior surfacealigned with the projections 8. The grooves 53 extend upwardly from theinner end of the valve stem 11 to a point slightly above the innermostface of the projections 8. Consequently, the grooves 53 form undercuts54 in the projections 8 the purpose of which will be described below. Astop 6 is provided at the inner end of each channel 7 to limit axialmovement of the valve stem 11 relative to the internal sleeve 12.

There is also provided adjacent the inner end 26 of the valve stem 11 astem cap 22. The stem cap 22 is slidably received within the internalsleeve 12. The stem cap 22 comprises a body portion 22 a, having afrusto-conically shaped recess 55 on its inner face, and a flange 22 b.The recess 55 mates against the conical portion 26 a of the valve stem11 in the non-dispensing position of FIG. 1. A spring 25 extends betweena base of the valve body 14 and the flange 22 b to bias the stem cap 22and valve stem 11 into the non-dispensing position, as shown in FIG. 1.

An inner seal 18 is sandwiched between the valve stem 11 and the flange22 b of the stem cap 22. The configuration of the inner seal 18 is shownin more detail in FIG. 5. The seal 18 is annular and is carried in useon the valve stem 11 so as to move axially therewith. The exterior faceis moulded to comprise two ribs 56, 57 with a recess 58 inbetween. Theinternal face comprises a recess 59 which can be used to accommodate anyunwanted flash produced during the moulding process so as to prevent theflash impinging on the internal sealing plane. Alternatively, the innerseal 18 may have a simplified construction without ribs so as to presenta substantially uninterrupted sealing surface.

The seal 18 is preferably made of an elastomer material. The inner seal18 seals against, in the non-dispensing position of FIG. 1, the internalsleeve 12. The inner seal 18 is slidable with respect to the internalsleeve 12 as will be discussed below.

In the non-dispensing position there is no open path from the meteringchamber 13 to the bore 4 of the valve stem 11, whereas there is an openpath from the interior of the canister to the metering chamber 13 viathe slots 31, and radial ports 23.

In use, the pressurised dispensing container is inverted such that thevalve stem 11 is lowermost in order that liquified propellant in thepressurised dispensing container collects at the end of the pressuriseddispensing container adjacent the metering valve 10 so as to flow intothe metering chamber 13 via the aforementioned pathway. The filling ofthe metering chamber 13 is very quick due to the sizing of the slots 31and radial ports 23.

Depression of the valve stem 11 relative to the internal sleeve 12 movesthe valve stem 11 inwardly into the container into the dispensingposition shown in FIG. 2. In the dispensing position the inner seal 18has moved past the radial ports 23 of the internal sleeve 12 to closeoff communication between the bulk product in the canister and themetering chamber 13. Further movement of the valve stem 11 in the samedirection to the dispensing position, as shown in FIG. 2, causes thedischarge port 21 to pass through the outer seal 17 into communicationwith the interior of the internal sleeve 12. At this point a path toatmosphere is established for discharging the product as follows.Product within the metering chamber 13 is able to exit the meteringchamber 13 though the radial ports 23 into the interior of the internalsleeve 12. From here the product flows between the internal sleeve 12and the valve stem 11, partially along the grooves 53 up towards theprojections 8. In the dispensing position of FIG. 2 the pips 50 of theprojections 8 are in contact with the stops 6 of the internal sleeve 12.Product passes between the stops 6 and the projections 8 via an openingwhich is formed because the undercut 54 extends the grooves 53 intocommunication with the gap 51 formed between the pips 50. Product thentraverses the channels 7 and into the bore 4 via the discharge ports 21.The product is then expelled to atmosphere via outer end 19 of the valvestem 11.

When the valve stem 11 is released, the biasing of the return spring 25causes the valve stem 11 to return to its original non-dispensingposition.

If the dispensing apparatus is returned to its upright position, asshown in FIG. 1, the product to be dispensed is free to return to thepressurised container. However, upon inversion of the apparatus into adispensing position, the metering chamber 13 will quickly be rechargedprior to the next actuation of the valve 10.

Advantageously, the inner seal 18 and the outer seal 17 are locatedoutside the metering chamber 13 and as such are not components whichform part of the construction of the metering chamber 13. Indeed in thefirst embodiment the metering chamber is constructed from only twocomponents, the valve body 14 and the internal sleeve 12. The outer seal17 is shielded from the metering chamber 13 by the flange 12 b of theinternal sleeve 12. The inner seal 18 is located within the internalsleeve on the valve stem 11 and not within the metering chamber 13 andoperatively seals the radial ports 23 by closing off the radial ports 23on the interior, radially innermost face of the internal sleeve 12 whichdoes not form a boundary surface of the metering chamber 13. Thus, themetering chamber volume is defined much more accurately since themetering chamber is wholly formed from materials which have highresistance to distortion and/or swelling and which are rigid. A furtheradvantage is that the metering chamber 13 does not contain any movingparts, in particular any part of the valve stem 11. This helps tomaintain the integrity of the metering chamber 13. In addition, thevalve of the present invention is particularly suited for very lowvolume metering where a small metering chamber is required. In typicalmetering valves moving parts within the metering chamber set a lowerlimit to the practical volume of the metering chamber since the movingparts (attached to the valve stem) require a minimum stroke length inorder for the valve to be actuatable. At present it is extremelydifficult to produce a metering chamber with a volume of less than 25microlitres. In the valve of the present invention there is notheoretical lower limit to the volume of the metering chamber since itdoes not contain any moving parts. Preferably the metering chamber has avolume up to 300 microlitres. More preferably, the metering chamber hasa volume up to 150 microlitres. Advantageously, the metering chamber mayhave a volume of up to 25 microlitres, preferably of 10 to 25microlitres. Very low volume capacities may be accommodated by partiallyfilling in or blocking off part of the annulus of the metering chamberso as to retain a minimum clearance distance between the radial innerand outer surfaces of the metering chamber.

In order to fill the canister with product prior to the first use of thedispensing apparatus, a pressure filling method is used, during whichthe product is blown under pressure into the valve 10 via the outlet 3of the valve stem 11 with the metering valve in the dispensing position.Under pressure the inner seal 18, together with the stem cap 22, areforced out of contact with the conical portion 26 a of the valve stem11, as shown in FIG. 3, allowing the product to pass between the innerseal 18 and the valve stem 11, through a central bore 46 formed in thestem cap 22 into the valve body 14 and thence into the container throughthe valve body openings 31.

FIGS. 6 to 8 show a second embodiment of metering valve according to thepresent invention. Like reference numerals have been used for likecomponents of the first embodiment. The valve 10 includes a valve stem11 which protrudes from and is axially slidable within a valve body 14.The valve stem 11 defines a hollow bore 4 having a discharge outlet 3 atits upper end. A chamber body 24 is slidably received in an inner end 26of the valve stem 11, which chamber body 24 is cup-shaped with an outerwall 28 which has a stepped profile. The interior surface of the valvestem 11 is provided with one or more longitudinal recesses 41 whichresult in the valve stem's interior having a ridged surface. Thelongitudinal recesses 41 form pathways or conduits between the valvestem 11 and the chamber body 24.

The chamber body 24 forms one of two components defining a meteringchamber 13 within the valve stem 11. The other component is a plug 45described below. The chamber 13 has a predefined volume whichcorresponds to a single dosage of the product to be dispensed. Thechamber body 24 is also provided with one or more inlets 30 at an innerend of the chamber body 24, i.e. furthest from the outlet 3. As with thefirst embodiment, locating the inlets 30 at the innermost end of thevalve helps to prevent entrapment of gas bubbles in the metering chamberon inversion of the valve prior to use.

An outer seal 17 is provided between the valve stem 11 and the valvebody 14 which seal 17 is in the form of an annular ring. The outer seal17 is supported by an annular insert 29 located adjacent the valve body14. The outer seal 17 is in sliding contact with the valve stem 11.

A base 34 of the valve body 14 is provided with an annular tubularextension 40 which extends into the interior of the valve 10 and whichis shaped so as to receive an inner end 46 of the chamber body 24. Theinner end 46 is provided with a plurality of slots 48 a defining aseries of legs 48 b of the chamber body 24. When the chamber body 24 isengaged in the tubular extension 40 the legs 48 b flex together toaccommodate the engagement. When the inner end 46 passes beyond theinner end of the tubular extension 40 the legs 48 b snap back intoplace. The chamber body 24 is provided with detents 47 to preventretraction of the chamber body 24 through the tubular extension 40. Thedetents 47 also hold the chamber body 24 in fixed spatial relationshipto the valve body 14.

The plug 45 is then inserted into the inner end 46 of the chamber body24. The plug 45 comprises external ribs 60 which are received in theslots 48 a. The plug 45 is retained as an interference fit. An upper end61 of the plug defines the inner end of the metering chamber 13.

The valve body 14 is positioned within a canister (not shown) containinga product to be dispensed. An inner end of the valve body 14 comprisesopenings 31 which allow passage of the product from the container intothe interior of the valve body 14 and vice versa. The valve 10 is heldin position with respect to the canister by means of a ferrule 15 whichis crimped to the top of the canister. Sealing between the valve body 14and the canister is provided by an annular gasket 16. The ferrule 15 isalso provided with an aperture 20 through which an outer end 19 of thevalve stem 11 protrudes.

An annular inner seal 18, typically of an elastomeric material, islocated around the chamber body 24 in close proximity to the inner end26 of the valve stem 11. The inner seal 18 is slidably moveable over thechamber body 24.

A spring 25 extends between the base 34 of the valve body 14 and a sealcarriage 50 positioned beneath the inner seal 18. The spring 25 biasesthe seal carriage 50 upwardly against the inner seal 18 to hold theinner seal 18 in contact with the inner end 26 of the valve stem 11, asshown in FIG. 6. Consequently, the spring 25 also biases the valve stem11 into the non-dispensing position. The metering chamber 13 is, in thenon-dispensing position of FIG. 6, sealed from the atmosphere by meansof the inner seal 18 which prevents leakage between the chamber body 24and the valve stem 11 and by means of the outer seal 17 which preventsleakage between the valve stem 11 and the valve body 14 or ferrule 15.

The metering valve 10 and the canister together form a dispensingapparatus. In the non-dispensing position of FIG. 6, there is no openpath from the metering chamber 13 to the bore 4 of the valve stem 11. Anopen path is established from the canister to the metering chamber 13via the openings 31 in the inner end of the valve body 14 and the inlets30.

In use, the dispensing apparatus is inverted such that the valve stem 11is lowermost in order that the liquified propellant in the pressuriseddispensing container collects at the end of the pressurised dispensingcontainer adjacent the metering valve 10 so as to flow into the meteringchamber 13 via the aforementioned open pathway.

The metering valve 10 is actuated by depression of the valve stem 11relative to the valve body 14. Upon depression the valve stem 11 movesinwardly into the valve and consequently moves relative to the chamberbody 24. This movement causes the inner seal 18 to pass across theinlets 30 as shown in FIG. 7 cutting off communication with the canisterand establishing an outlet pathway from the metering chamber 13 to thebore 4 of the valve stem 11 via the inlets 30 and the longitudinalrecesses 41 formed on the interior surface of the valve stem 11.Establishment of the outlet pathway allows the product in the meteringchamber 13 to be discharged to the atmosphere by volatilisation of theliquified propellant.

When the valve stem 11 is released, the biasing of the spring 25 causesthe seal carriage 50, inner seal 18 and valve stem 11 to return to theiroriginal positions. As a result, the inner seal 18 returns to itsnon-dispensing position above the inlet 30 allowing product in thepressurised dispensing container to pass into the metering chamber 13 onthe next inversion of the apparatus in order to recharge the chamber inreadiness for further dispensing operations.

If the dispensing apparatus is returned to its upright position, asshown in FIG. 6, the product to be dispensed is free to return to thepressurised container. However, upon inversion of the apparatus into adispensing position, the metering chamber will very quickly be rechargedprior to actuation of the valve 10.

Advantageously, the inner seal 18 and the outer seal 17 are locatedoutside the metering chamber 13 and as such are not themselvescomponents of the construction of the metering chamber 13. The outerseal 17 is remote from the metering chamber 13. The inner seal 18operatively seals the ports 30 by closing off the ports 30 on theexterior face of the chamber body 24 which does not form a boundarysurface of the metering chamber 13. Thus, the metering chamber volume isdefined much more accurately since the metering chamber is defined bysurfaces formed from materials which have high resistance to distortionand/or swelling. Indeed in the second embodiment the metering chamber isconstructed from only two components, the chamber body 24 and the plug45. A further advantage is that the metering chamber 13 does not containany moving parts, in particular any part of the valve stem 11. Ratherthe metering chamber is located within the valve stem. This helps tomaintain the integrity of the metering chamber 13.

In order to fill the container with a product prior to the first use ofthe dispensing apparatus, a pressure filling method is used, as shown inFIG. 8. During the filling process, the product is blown under pressureinto the valve 10 via the outlet 3 of the valve stem 11 with the valvestem 11 held in the actuated position of FIG. 7. Under pressure theinner seal 18 is forced inwardly into the valve to thereby move past theinlets 30 of the chamber body 24, as shown in FIG. 8. This movement isaccommodated by movement of the seal carriage 50 against the bias of thespring 25. Product is thus able to pass through the hollow bore 4 of thevalve stem 11, along the longitudinal recesses 41 and through theapertures 31 in the inner part of the valve body 14.

As with the first embodiment the volume of the metering chamber mayadvantageously be chosen with a degree of flexibility. Preferably themetering chamber has a volume up to 125 microlitres where the chamber iswithin the valve stem. Advantageously, the metering chamber may have avolume up to 25 microlitres, preferably of 10 to 25 microlitres.

The seals 17 and/or 18 of both embodiments may be formed from materialhaving acceptable performance characteristics. Preferred examplesinclude nitrile, EPDM and other thermoplastic elastomers, butyl andneoprene.

Other rigid components of the metering valve of both embodiments, suchas the valve body 14, internal sleeve 12, chamber body 24 and valve stem11 may be formed, for example, from polyester, nylon, acetal or similar.Alternative materials for the rigid components include stainless steel,ceramics and glass.

1. A metering valve comprising a valve stem co-axially slidable within avalve body, the metering valve comprising a metering chamber wherein themetering chamber is static and no part of the valve stem defines themetering chamber, and the metering chamber is constructed wholly fromrigid components.
 2. A metering valve as claimed in claim 1 wherein themetering chamber is constructed wholly from components formed from oneor more materials selected from polyester, nylon, acetal, stainlesssteel, ceramics or glass.
 3. A metering valve as claimed in claim 1further comprising inner and outer seals external to the meteringchamber.
 4. A metering valve as claimed in claim 1 wherein the meteringchamber is constructed from only two rigid components.
 5. A meteringvalve as claimed in claim 1 wherein the components of the meteringchamber comprises one or more stops for limiting axial movement of thevalve stern therethrough.
 6. A metering valve as claimed in claim 1wherein the metering chamber surrounds the valve stem.
 7. A meteringvalve as claimed in claim 1 wherein the metering chamber is annular. 8.A metering valve as claimed in any preceding claim wherein the valvebody defines a radially outermost surface of the metering chamber.
 9. Ametering valve as claimed in claim 1 wherein the metering chamber has adosage volume that is designed to correspond with a single dosedischarge volume to be discharged by the metering valve when themetering valve is placed in an outlet access state.
 10. A metering valveas claimed in claim 1 further comprising an internal sleeve.
 11. Ametering valve as claimed in claim 10 wherein the internal sleeve islocated concentrically within the valve body.
 12. A metering valve asclaimed in claim 10 wherein the metering chamber is formed between thevalve body and the internal sleeve.
 13. A metering valve as claimed inclaim 10 wherein the internal sleeve defines a radially innermostsurface of the metering chamber.
 14. A metering chamber as claimed inclaim 10 wherein the internal sleeve comprises a cylindrical portion.15. A metering valve as claimed in claim 10 wherein the inner seal iscarried on the valve stem in sliding sealing contact with a radiallyinnermost surface of the internal sleeve, being external the meteringchamber.
 16. A metering valve as claimed in claim 10 wherein a radiallydirected flange of the internal sleeve defines an outer end surface ofthe metering chamber.
 17. A metering valve as claimed in claim 10wherein the valve stem is adjustably received by the internal sleevesuch that, when said metering valve is in use, said valve stem movesrelative to a more stationary internal sleeve.
 18. A metering valve asclaimed in claim 10 wherein the internal sleeve surrounds the valvestem.
 19. A metering valve as claimed in claim 18 wherein the internalsleeve separates the metering chamber from the valve stem.
 20. Ametering valve as claimed in claim 10 wherein the internal sleevecomprises one or more ports for passage of a product into or out of themetering chamber.
 21. A metering valve as claimed in claim 20 whereinthe one or more ports each function as both an inlet to, and an outletfrom, the metering chamber in use.
 22. A metering valve as claimed inclaim 20 wherein the one or more ports are located at an inner end ofthe metering chamber.
 23. A metering valve as claimed in claim 20wherein the one or more ports are static.
 24. A metering valve asclaimed in claim 1 wherein the metering chamber has a volume of up to300 microlitres.
 25. A metering valve as claimed in claim 24 wherein themetering chamber has a volume up to 25 microlitres.
 26. A metering valveas claimed in claim 25 wherein the metering chamber has a volume of 10to 25 microlitres.
 27. A metering valve comprising a valve stemco-axially slidable within a valve body, the metering valve comprising ametering chamber wherein the metering chamber is static in that itcontains no part of the valve stem and is constructed wholly from rigidcomponents, and said metering valve further comprising an internalsleeve, and wherein a radially directed flange of the valve body definesan inner end surface of the metering chamber.
 28. A metering valvecomprising a valve stem co-axially slidable within a valve body, themetering valve comprising a metering chamber wherein the meteringchamber is static in that it contains no part of the valve stem and isconstructed wholly from rigid components; and wherein the meteringchamber is located within the valve stem such that product held in themetering chamber is dischargeable directly into the valve stem.
 29. Ametering valve as claimed in claim 28 wherein the metering chamber iscylindrical.
 30. A metering valve as claimed in claim 28 wherein themetering chamber comprises one or more ports which each function as bothan inlet to, and an outlet from, the metering chamber in use.
 31. Ametering valve as claimed in claim 30 wherein the one or more ports arelocated at an inner end of the metering chamber.
 32. A metering valve asclaimed in claim 28 further comprising a seal which is movable relativeto the metering chamber to close off said one or more ports, whereinsaid seal is external to said metering chamber.
 33. A metering valve asclaimed in claim 32 wherein said seal surrounds said metering chamber.34. A metering valve as claimed in claim 28 wherein the metering chamberis constructed from an open-ended chamber body and a plug.
 35. Ametering valve as claimed in claim 34 wherein the chamber body issubstantially located within the valve stem.
 36. A metering valvecomprising a valve stem co-axially slidable within a valve body, themetering valve comprising a metering chamber wherein the meteringchamber is static in that it contains no part of the valve stem and isconstructed wholly from rigid components; and wherein the meteringchamber has no moving parts therein.
 37. A metering valve comprising avalve stem co-axially slidable within a valve body, the metering valvecomprising a metering chamber wherein the metering chamber is static inthat it contains no part of the valve stem and is constructed whollyfrom rigid components, and said metering valve further comprising one ormore seals, and said metering chamber being arranged as to preclude anyseal material from bounding and defining the metering chamber.
 38. Ametering valve as recited in claim 37, further comprising a product,which product is contained in said metering chamber, and which productis a pharmaceutical product comprising a propellant.